The dark patch that can be seen on this sandstone boulder is the result of an epilithic cyanobacterial community colonizing the surface. There are four major lithic (rock) habitats found in the Antarctic: epilithic, the exposed surface of rocks, chasmolithic, the fissures and cracks within the rocks, cryptoendolithic, the internal airspaces within the rock between crystals and hypolithic, the underneath side of the rocks.